The present invention relates to a process for producing p-tolualdehyde which comprises reacting toluene with carbon monoxide in the presence of a hydrogen fluoride-boron trifluoride catalyst.
Japanese Pat. Publication No. 29760/1964 discloses a process for producing p-tolualdehyde which comprises reacting toluene with carbon monoxide in the presence of a hydrogen fluoride-boron trifluoride catalyst. In other words, the invention of Japanese Pat. Publication No. 29760/1964 relates to a process for producing p-tolualdehyde which comprises adding all the necessary boron trifluoride to a mixture of the toluene and an excess amount of hydrogen fluoride to form a toluene-hydrogen fluoride-boron trifluoride complex and then introducing carbon monoxide to the complex to convert the toluene to p-tolualdehyde. In such process disclosed in the Japanese Patent Publication, the reaction of the carbon monoxide with the toluene is effected at a temperature below room temperature in order to avoid any change in quality of the object product, namely p-tolualdehyde. P-tolualdehyde can be produced in a good yield by adjusting the molar ratio of the catalysts to toluene to be within a determined range.
However, according to the invention of the Japanese Patent Publication, all the amount of boron trifluoride necessary to convert a substantial amount of toluene to p-tolualdehyde is introduced to a toluene-hydrogen fluoride mixture, thereby forming a toluene-hydrogen fluoride-boron trifluoride complex, and thereafter carbon monoxide is introduced to the complex to effect the reaction of toluene with carbon monoxide. In such process, since the vapor pressure of the toluene-hydrogen fluoride-boron trifluoride complex is high, it is necessary to introduce the boron trifluoride to the mixture of toluene and hydrogen fluoride at a relatively high pressure in order to add all the necessary amount of boron trifluoride to the mixture. But, since boron trifluoride which is a catalyst is highly corrosive, it is difficult to make an apparatus for compressing corrosive boron trifluoride.
It is preferable to introduce boron trifluoride to a toluene-hydrogen fluoride mixture at a pressure lower than one at which p-tolualdehyde-hydrogen fluoride-boron trifluoride complex is decomposed in a decomposition column. When all the necessary amount of boron trifluoride is added to the toluene-hydrogen fluoride mixture, the vapor pressure of the toluene-hydrogen fluoride-boron trifluoride complex becomes high. In order to introduce boron trifluoride withdrawn from the decomposition column to the toluene-hydrogen fluoride mixture without compressing it, it is necessary to raise the decomposition pressure. However when the decomposition pressure is too high, a change in quality of p-tolualdehyde and polymerization of the aldehyde are generally prone to occur in the decomposition column.
This invention eliminates the above mentioned disadvantages.
The conversion of toluene to p-tolualdehyde depends upon the amount of boron trifluoride added to the reaction system. When all the boron trifluoride necessary to convert a substantial amount of toluene to p-tolualdehyde is introduced to a toluene-hydrogen fluoride mixture, the vapor pressure of the resulting toluene-hydrogen fluoride-boron trifluoride complex becomes high.
It was found that the vapor pressure of a mixture of toluene, hydrogen fluoride and boron trifluoride is in proportion to the amount of boron trifluoride present in the mixture, especially the ratio of the boron trifluoride to the hydrogen fluoride. We, the inventors, have found that when only part of the boron trifluoride necessary to convert a substantial amount of toluene to p-tolualdehyde is introduced to a mixture of toluene and hydrogen fluoride, the vapor pressure of the mixture does not become high. Furthermore, we have found a process for introducing the necessary amount of boron trifluoride to the mixture of toluene and hydrogen fluoride at a relatively low pressure, in which part of the necessary amount of boron trifluoride is added to the mixture, and then part of the toluene reacts with the carbon monoxide, and thereafter the remainder of the boron trifluoride is added to the mixture. This invention was formed on the basis of these discoveries.
Therefore, it is an object of this invention to provide a process for producing p-tolualdehyde in which boron trifluoride to be used as a catalyst can be added to a mixture of toluene and hydrogen fluoride at a relatively low pressure.
It is a further object of the invention to provide a process for producing p-tolualdehyde in which boron trifluoride to be used as a catalyst can be introduced to the mixture at a pressure lower than one at which the decomposition of p-tolualdehyde is effected.
It is another object of the invention to provide a two-step process for producing p-tolualdehyde.
Other object of the invention will in part be obvious and will in part appear hereinafter.